1. Field of the Invention
The present invention relates generally to radio frequency identification (RFID) applications, and more particularly to systems and methods of beamforming in RFID applications.
2. Description of Related Art
Many radio frequency identification systems use batteryless tags that can be identified by a reader through radio frequency communication to label items. In these systems, an RFID reader (comprising a radio frequency transmitter and receiver) energizes the tag and then receives data from the tag. Conventional readers for passive RFID systems typically operate by the RFID reader first sending an unmodulated radio frequency (RF) signal to power the tag; then sending interrogation data to the tag; and then receiving modulated backscatter back from the tag. The maximum read range of an RFID reader is typically limited by the power needed to energize the tag and to generate the backscatter response. Additionally, the read range and reliability varies significantly depending upon the scattering environment. Thus, the location of the RFID reader's antenna(s) (and/or antenna elements) has to be carefully positioned and/or tuned by experts to optimize performance in settings such as, for example, a factory floor, a production facility, or a commercial establishment.
Antenna beamforming comprises using two or more antennas (or antenna elements) to direct electromagnetic energy to a certain region in space. Using beamforming, the direction of a beam of electromagnetic energy can be varied electronically by selecting the gains and phases of the signals fed to each of the two or more antennas. By using more antennas, the beam of electromagnetic energy can be made narrower, thus increasing the total energy directed to a certain region in space, such as a desired surface. Antenna beamforming is used in such systems as cellular phone base stations and wireless local area network (LAN) base stations.
Conventional RFID systems connect the antenna elements to the transmitter and receiver through coaxial cables designed for carrying high frequency electrical signals. The RFID reader may control the input phase into each of the antenna elements to achieve the desired beam directionality. However, there are a number of problems with the conventional approach. For example, coaxial cable is bulky and expensive. In addition, the users of these systems must manually configure and/or tune the RFID reader's antennas to direct the electromagnetic beam in a desired direction. This manual configuration and/or tuning is time consuming and requires technicians skilled in radio frequency technology. Moreover, the configuration and/or tuning may no longer function when there are changes in the radio frequency environment or when the RFID tags are in motion.